Magnetic random access memory with perpendicular enhancement layer

ABSTRACT

The present invention is directed to an MTJ memory element including a magnetic free layer structure which includes one or more magnetic free layers that have a same variable magnetization direction substantially perpendicular to layer planes thereof; an insulating tunnel junction layer formed adjacent to the magnetic free layer structure; a magnetic reference layer structure comprising a first magnetic reference layer formed adjacent to the insulating tunnel junction layer and a second magnetic reference layer separated therefrom by a perpendicular enhancement layer with the first and second magnetic reference layers having a first fixed magnetization direction substantially perpendicular to layer planes thereof; an anti-ferromagnetic coupling layer formed adjacent to the second magnetic reference layer opposite the perpendicular enhancement layer; and a magnetic fixed layer comprising first and second magnetic fixed sublayers with the second magnetic fixed sublayer formed adjacent to the anti-ferromagnetic coupling layer opposite the second magnetic reference layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of the commonlyassigned application bearing Ser. No. 14/560,740 filed on Dec. 4, 2014by Gan et al. and entitled “Magnetic Random Access Memory WithPerpendicular Enhancement Layer,” which is a continuation-in-part of thecommonly assigned application bearing Ser. No. 14/256,192 filed on Apr.18, 2014 by Gan et al. and entitled “Magnetic Random Access Memory WithPerpendicular Enhancement Layer,” which is a continuation-in-part of thecommonly assigned application bearing Ser. No. 14/053,231 filed on Oct.14, 2013 by Gan et al. and entitled “Magnetic Random Access MemoryHaving Perpendicular Enhancement Layer,” which is a continuation-in-partof the commonly assigned application bearing Ser. No. 14/026,163 filedon Sep. 13, 2013 by Gan et al. and entitled “Perpendicular STTMRAMDevice with Balanced Reference Layer,” which is a continuation-in-partof the commonly assigned application bearing Ser. No. 13/029,054 filedon Feb. 16, 2011 by Zhou et al. and entitled “Magnetic Random AccessMemory With Field Compensating Layer and Multi-Level Cell,” and acontinuation-in-part of the commonly assigned application bearing Ser.No. 13/277,187 filed on Oct. 19, 2011 by Huai et al. and entitled“Memory System Having Thermally Stable Perpendicular Magneto TunnelJunction (MTJ) and A Method of Manufacturing Same,” which claimspriority to U.S. Provisional Application No. 61/483,314. All of theseapplications are incorporated herein by reference, including theirspecifications. The present application is related to the commonlyassigned copending application bearing Ser. No. 13/737,897 filed on Jan.9, 2013, the commonly assigned copending application bearing Ser. No.14/021,917 filed on Sep. 9, 2013, the commonly assigned copendingapplication bearing Ser. No. 13/099,321 filed on May 2, 2011, thecommonly assigned copending application bearing Ser. No. 13/928,263filed on Jun. 26, 2013, the commonly assigned copending applicationbearing Ser. No. 14/173,145 filed on Feb. 5, 2014, the commonly assignedcopending application bearing Ser. No. 14/195,427 filed on Mar. 3, 2014,the commonly assigned copending application bearing Ser. No. 14/198,405filed on Mar. 5, 2014, and the commonly assigned copending applicationbearing Ser. No. 14/255,884 filed on Apr. 17, 2014.

BACKGROUND

The present invention relates to a magnetic random access memory (MRAM)device, and more particularly, to a spin transfer torque MRAM deviceincluding at least a perpendicular enhancement layer in its memoryelement.

Spin transfer torque magnetic random access memory (STT-MRAM) is a newclass of non-volatile memory, which can retain the stored informationwhen powered off. An STT-MRAM device normally comprises an array ofmemory cells, each of which includes at least a magnetic memory elementand a selection element coupled in series between appropriateelectrodes. Upon application of an appropriate voltage or current to themagnetic memory element, the electrical resistance of the magneticmemory element would change accordingly, thereby switching the storedlogic in the respective memory cell.

FIG. 1 is a schematic circuit diagram of a conventional STT-MRAM device30, which comprises a plurality of memory cells 32, each of the memorycells 32 including a selection transistor 34 coupled to a magneticmemory element 36; a plurality of parallel word lines 38 with each beingcoupled to the gates of a respective row of the selection transistors 34in a first direction; and a plurality of parallel bit lines 40 with eachbeing coupled to a respective row of the memory elements 36 in a seconddirection perpendicular to the first direction; and optionally aplurality of parallel source lines 42 with each being coupled to arespective row of the selection transistors 34 in the first or seconddirection.

FIG. 2 shows a conventional magnetic memory element comprising amagnetic reference layer 50 and a magnetic free layer 52 with aninsulating tunnel junction layer 54 interposed therebetween, therebycollectively forming a magnetic tunneling junction (MTJ) 56. Themagnetic reference layer 50 and free layer 52 have magnetizationdirections 58 and 60, respectively, which are substantiallyperpendicular to the respective layer planes. Therefore, the MTJ 56 is aperpendicular type comprising the magnetic layers 50 and 52 withperpendicular anisotropy. Upon application of an appropriate currentthrough the perpendicular MTJ 56, the magnetization direction 60 of themagnetic free layer 52 can be switched between two directions: paralleland anti-parallel with respect to the magnetization direction 58 of themagnetic reference layer 50. The insulating tunnel junction layer 54 isnormally made of a dielectric material with a thickness ranging from afew to a few tens of angstroms. However, when the magnetizationdirections 60 and 58 of the magnetic free layer 52 and reference layer50 are substantially parallel, electrons polarized by the magneticreference layer 50 may tunnel through the insulating tunnel junctionlayer 54, thereby decreasing the electrical resistivity of theperpendicular MTJ 56. Conversely, the electrical resistivity of theperpendicular MTJ 56 is high when the magnetization directions 58 and 60of the magnetic reference layer 50 and free layer 52 are substantiallyanti-parallel. Accordingly, the stored logic in the magnetic memoryelement can be switched by changing the magnetization direction 60 ofthe magnetic free layer 52.

One of many advantages of STT-MRAM over other types of non-volatilememories is scalability. As the size of the perpendicular MTJ 56 isreduced, the current required to switch the magnetization direction 60of the magnetic free layer 52 is reduced accordingly, thereby reducingpower consumption. However, the thermal stability of the magnetic layers50 and 52, which is required for long term data retention, also degradeswith miniaturization of the perpendicular MTJ 56.

For the foregoing reasons, there is a need for an STT-MRAM device thathas a thermally stable perpendicular MTJ memory element and that can beinexpensively manufactured.

SUMMARY

The present invention is directed to a spin transfer torque (STT)magnetic random access memory (MRAM) element that satisfies this need.An STT-MRAM element having features of the present invention includes amagnetic tunnel junction (MTJ) structure formed between an optional seedlayer and an optional cap layer. The MTJ structure comprises a magneticfree layer structure and a magnetic reference layer structure with aninsulating tunnel junction layer interposed therebetween, and a magneticfixed layer separated from the magnetic reference layer structure by ananti-ferromagnetic coupling layer.

The magnetic free layer structure may comprise one or more magnetic freelayers having a same variable magnetization direction perpendicular tothe layer planes thereof. In an embodiment, the magnetic free layerstructure includes a perpendicular enhancement layer formed between twomagnetic free layers. The magnetic reference layer structure maycomprise one or more magnetic reference layers having a first fixedmagnetization direction perpendicular to the layer planes thereof. Inanother embodiment, the magnetic reference layer structure includes aperpendicular enhancement layer formed between two magnetic referencelayers. The magnetic fixed layer may comprise one or more magneticsublayers having a second fixed magnetization direction that issubstantially perpendicular to the layer planes thereof and issubstantially opposite to the first fixed magnetization direction. Instill another embodiment, the magnetic fixed layer includes aperpendicular enhancement layer formed between two magnetic fixedsublayers.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 is a schematic circuit diagram of a conventional STT-MRAM device;

FIG. 2 is a cross-sectional view of a conventional magnetic memoryelement comprising a perpendicular magnetic tunnel junction (MTJ);

FIGS. 3A and 3B are cross-sectional views of a first embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 4A and 4B are cross-sectional views of a second embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 5A and 5B are cross-sectional views of a third embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 6A and 6B are cross-sectional views of a fourth embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 7A and 7B are cross-sectional views of a fifth embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 8A and 8B are cross-sectional views of a sixth embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 9A and 9B are cross-sectional views of a seventh embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 10A and 10B are cross-sectional views of an eighth embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 11A and 11B are cross-sectional views of a ninth embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 12A and 12B are cross-sectional views of a tenth embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 13A and 13B are cross-sectional views of an eleventh embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 14A and 14B are cross-sectional views of a twelfth embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 15A and 15B are cross-sectional views of exemplary MTJ structurescorresponding to the fifth embodiment of the present invention;

FIGS. 16A and 16B are cross-sectional views of exemplary magnetic freelayer structures corresponding to various embodiments of the presentinvention;

FIGS. 17A and 17B are cross-sectional views of exemplary magneticreference layer structures corresponding to various embodiments of thepresent invention;

FIGS. 18A and 18B are cross-sectional views of exemplary structures thatinclude magnetic reference layer structure and magnetic fixed layer inaccordance with various embodiments of the present invention;

FIGS. 19A and 19B are cross-sectional views of the exemplary MTJstructures in which the magnetic reference layer structure includes thefirst and second magnetic reference layers without a perpendicularenhancement layer interposed therebetween; and

FIGS. 20A and 20B are cross-sectional views of a thirteenth embodimentof the present invention as applied to a perpendicular MTJ memoryelement.

For purposes of clarity and brevity, like elements and components willbear the same designations and numbering throughout the Figures, whichare not necessarily drawn to scale.

DETAILED DESCRIPTION

In the Summary above and in the Detailed Description, and the claimsbelow, and in the accompanying drawings, reference is made to particularfeatures of the invention. It is to be understood that the disclosure ofthe invention in this specification includes all possible combinationsof such particular features. For example, where a particular feature isdisclosed in the context of a particular aspect or embodiment of theinvention, or a particular claim, that feature can also be used, to theextent possible, in combination with and/or in the context of otherparticular aspects and embodiments of the invention, and in theinvention generally.

Where reference is made herein to a material AB composed of element Aand element B, the material AB may be an alloy, a compound, or acombination thereof, unless otherwise specified or the context excludesthat possibility.

Where reference is made herein to a multilayer structure [C/D] formed byinterleaving layer(s) of material C with layer(s) of material D, atleast one of material C and material D may be made of elemental metal,elemental non-metal, alloy, or compound. The multilayer structure [C/D]may contain any number of layers but may have as few as two layersconsisting of one layer of material C and one layer of material D. Themultilayer structure [C/D] has a stack structure that may begin with onematerial and end with the other material such as C/D/C/D or may beginwith one material and end with the same material such as C/D/C.Individual layers of material C may or may not have the same thickness.Likewise, individual layers of material D may or may not have the samethickness. The multilayer structure [C/D] may or may not exhibit thecharacteristic satellite peaks associated with superlattice whenanalyzed by X-ray or neutron diffraction.

The term “noncrystalline” means an amorphous state or a state in whichfine crystals are dispersed in an amorphous matrix, not a single crystalor polycrystalline state. In case of state in which fine crystals aredispersed in an amorphous matrix, those in which a crystalline peak issubstantially not observed by, for example, X-ray diffraction can bedesignated as “noncrystalline.”

The term “magnetic dead layer” means a layer of supposedly ferromagneticmaterial that does not exhibit a net magnetic moment in the absence ofan external magnetic field. A magnetic dead layer of several atomiclayers may form in a magnetic film in contact with another layermaterial owing to intermixing of atoms at the interface. Alternatively,a magnetic dead layer may form as thickness of a magnetic film decreasesto a point that the magnetic film becomes superparamagnetic.

A first embodiment of the present invention as applied to aperpendicular MTJ memory element that includes at least a perpendicularenhancement layer (PEL) to improve the perpendicular anisotropy ofmagnetic layers adjacent thereto will now be described with reference toFIG. 3A. Referring now to FIG. 3A, the illustrated memory element 114includes a magnetic tunnel junction (MTJ) structure 116 in between anoptional seed layer 118 and an optional cap layer 120. The MTJ structure116 comprises a magnetic free layer structure 122 and a magneticreference layer structure 124 with an insulating tunnel junction layer126 interposed therebetween. The magnetic reference layer structure 124and the magnetic free layer structure 122 may be formed adjacent to theoptional seed layer 118 and cap layer 120, respectively.

The magnetic free layer structure 122 includes a first magnetic freelayer 128 formed adjacent to the insulating tunnel junction layer 126and a second magnetic free layer 130 separated from the first magneticfree layer 128 by a first perpendicular enhancement layer (PEL) 132. Thefirst and the second magnetic free layers 128 and 130 have respectivelyfirst and second variable magnetization directions 129 and 131substantially perpendicular to the layer planes thereof. The firstmagnetic free layer 128 may comprise one or more magnetic sublayershaving the first variable magnetization direction 129. Likewise, thesecond magnetic free layer 130 may comprise one or more magneticsublayers having the second variable magnetization direction 131. Thefirst and the second variable magnetization directions 129 and 131 maybe parallel or anti-parallel to each other.

The magnetic reference layer structure 124 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by a second perpendicular enhancementlayer 138. The first and second magnetic reference layers 134 and 136have a first fixed magnetization direction 125 substantiallyperpendicular to the layer planes thereof. The first magnetic referencelayer 134 may comprise one or more magnetic sublayers having the firstfixed magnetization direction 125. Similarly, the second magneticreference layer 136 may comprise one or more magnetic sublayers havingthe first fixed magnetization direction 125.

The stacking order of the individual layers in the MTJ structure 116 ofthe memory element 114 may be inverted as illustrated in FIG. 3B withoutaffecting the device performance. The memory element 114′ of FIG. 3B hasan MTJ structure 116′ that has the same layers but with the invertedstacking order comparing to the MTJ structure 116. Accordingly, themagnetic free layer structure 122 and the magnetic reference layerstructure 124 may be formed adjacent to the optional seed layer 118 andcap layer 120, respectively.

A second embodiment of the present invention as applied to an MTJ memoryelement is illustrated in FIG. 4A. The memory element 140 includes amagnetic tunnel junction (MTJ) structure 142 in between an optional seedlayer 118 and an optional cap layer 120. The MTJ structure 142 comprisesa magnetic free layer structure 122 and a magnetic reference layer 144with an insulating tunnel junction layer 126 interposed therebetween.The magnetic reference layer 144 and the magnetic free layer structure122 may be formed adjacent to the optional seed layer 118 and cap layer120, respectively.

The magnetic free layer structure 122 includes a first magnetic freelayer 128 formed adjacent to the insulating tunnel junction layer 126and a second magnetic free layer 130 separated from the first magneticfree layer 128 by a perpendicular enhancement layer (PEL) 132. The firstand the second magnetic free layers 128 and 130 have respectively firstand second variable magnetization directions 129 and 131 substantiallyperpendicular to the layer planes thereof. The first magnetic free layer128 may comprise one or more magnetic sublayers having the firstvariable magnetization direction 129. Likewise, the second magnetic freelayer 130 may comprise one or more magnetic sublayers having the secondvariable magnetization direction 131. The first and the second variablemagnetization directions 129 and 131 may be parallel or anti-parallel toeach other.

The magnetic reference layer 144 has a first fixed magnetizationdirection 145 substantially perpendicular to the layer plane thereof.The magnetic reference layer 144 may comprise one or more magneticsublayers having the first fixed magnetization direction 145.

The stacking order of the individual layers in the MTJ structure 142 ofthe memory element 140 may be inverted as illustrated in FIG. 4B withoutaffecting the device performance. The memory element 140′ of FIG. 4B hasan MTJ structure 142′ that has the same layers but with the invertedstacking order comparing to the MTJ structure 142. Accordingly, themagnetic free layer structure 122 and the magnetic reference layer 144may be formed adjacent to the optional seed layer 118 and cap layer 120,respectively.

A third embodiment of the present invention as applied to an MTJ memoryelement is illustrated in FIG. 5A. The memory element 150 includes amagnetic tunnel junction (MTJ) structure 152 in between an optional seedlayer 118 and an optional cap layer 120. The MTJ structure 152 comprisesa magnetic free layer 154 and a magnetic reference layer structure 124with an insulating tunnel junction layer 126 interposed therebetween.The magnetic reference layer structure 124 and the magnetic free layer154 may be formed adjacent to the optional seed layer 118 and cap layer120, respectively.

The magnetic free layer 154 has a variable magnetization direction 155substantially perpendicular to the layer plane thereof. The magneticfree layer 154 may comprise one or more magnetic sublayers having thevariable magnetization direction 155.

The magnetic reference layer structure 124 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by a perpendicular enhancement layer138. The first and second magnetic reference layers 134 and 136 have afirst fixed magnetization direction 125 substantially perpendicular tothe layer planes thereof. The first magnetic reference layer 134 maycomprise one or more magnetic sublayers having the first fixedmagnetization direction 125. Similarly, the second magnetic referencelayer 136 may comprise one or more magnetic sublayers having the firstfixed magnetization direction 125.

The stacking order of the individual layers in the MTJ structure 152 ofthe memory element 150 may be inverted as illustrated in FIG. 5B withoutaffecting the device performance. The memory element 150′ of FIG. 5B hasan MTJ structure 152′ that has the same layers but with the invertedstacking order comparing to the MTJ structure 152. Accordingly, themagnetic free layer 154 and the magnetic reference layer structure 124may be formed adjacent to the optional seed layer 118 and cap layer 120,respectively.

The optional seed layer 118 of the memory elements 114, 114′, 140, 140′,150, and 150′ of FIGS. 3A, 3B, 4A, 4B, 5A, and 5B, respectively, mayfacilitate the optimal growth of magnetic layers formed thereon toincrease perpendicular anisotropy. The seed layer 118 may also serve asa bottom electrode to the MTJ structures 116, 116′, 142, 142′, 152, and152′. The seed layer 118 may comprise one or more seed sublayers, whichmay be formed adjacent to each other.

The optional cap layer 120 of the memory elements 114, 114′, 140, 140′,150, and 150′ of FIGS. 3A, 3B, 4A, 4B, 5A, and 5B, respectively, mayfunction as a top electrode for the MTJ structures 116, 116′, 142, 142′,152, and 152′ and may also improve the perpendicular anisotropy of themagnetic layer formed adjacent thereto during annealing. The cap layer120 may comprise one or more cap sublayers, which may be formed adjacentto each other.

For the MTJ structures 116, 116′, 142, 142′, 152, and 152′ of FIGS. 3A,3B, 4A, 4B, 5A, and 5B, the magnetic free layer structure 122 and themagnetic reference layer structure 124 include therein the perpendicularenhancement layers 132 and 138, respectively. The perpendicularenhancement layers 132 and 138 may further improve the perpendicularanisotropy of the magnetic layers formed adjacent thereto duringdeposition or annealing or both. Each of the perpendicular enhancementlayers 132 and 138 may have a single layer structure or may comprisemultiple perpendicular enhancement sublayers, which may be formedadjacent to each other.

A fourth embodiment of the present invention as applied to an MTJ memoryelement is illustrated in FIG. 6A. The memory element 160 includes amagnetic tunnel junction (MTJ) structure 162 in between an optional seedlayer 118 and an optional cap layer 120. The MTJ structure 162 comprisesa magnetic free layer structure 122 and a magnetic reference layerstructure 124 with an insulating tunnel junction layer 126 interposedtherebetween, an anti-ferromagnetic coupling layer 164 formed adjacentto the magnetic reference layer structure 124, and a magnetic fixedlayer 166 formed adjacent to the anti-ferromagnetic coupling layer 164.The magnetic fixed layer 166 and the magnetic free layer structure 122may be formed adjacent to the optional seed layer 118 and cap layer 120,respectively. The memory element 160 of FIG. 6A is different from thememory element 114 of FIG. 3A in that the anti-ferromagnetic couplinglayer 164 and the magnetic fixed layer 166 have been inserted in betweenthe optional seed layer 118 and the magnetic reference layer structure124.

The magnetic free layer structure 122 includes a first magnetic freelayer 128 formed adjacent to the insulating tunnel junction layer 126and a second magnetic free layer 130 separated from the first magneticfree layer 128 by a first perpendicular enhancement layer (PEL) 132. Thefirst and the second magnetic free layers 128 and 130 have respectivelyfirst and second variable magnetization directions 129 and 131substantially perpendicular to the layer planes thereof. The firstmagnetic free layer 128 may comprise one or more magnetic sublayershaving the first variable magnetization direction 129. Likewise, thesecond magnetic free layer 130 may comprise one or more magneticsublayers having the second variable magnetization direction 131. Thefirst and the second variable magnetization directions 129 and 131 maybe parallel or anti-parallel to each other.

The magnetic reference layer structure 124 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by a second perpendicular enhancementlayer 138. The first and second magnetic reference layers 134 and 136have a first fixed magnetization direction 125 substantiallyperpendicular to the layer planes thereof. Each of the first magneticreference layer 134 and the second magnetic reference layer 136 maycomprise one or more magnetic sublayers having the first fixedmagnetization direction 125.

The magnetic fixed layer 166 has a second fixed magnetization direction167 that is substantially perpendicular to the layer plane thereof andis substantially opposite to the first fixed magnetization direction125. The magnetic fixed layer 166 may comprise one or more magneticsublayers having the second fixed magnetization direction 167.

The stacking order of the individual layers in the MTJ structure 162 ofthe memory element 160 may be inverted as illustrated in FIG. 6B withoutaffecting the device performance. The memory element 160′ of FIG. 6B hasan MTJ structure 162′ that has the same layers but with the invertedstacking order comparing to the MTJ structure 162. Accordingly, themagnetic free layer structure 122 and the magnetic fixed layer 166 maybe formed adjacent to the optional seed layer 118 and cap layer 120,respectively.

A fifth embodiment of the present invention as applied to an MTJ memoryelement is illustrated in FIG. 7A. The memory element 170 includes amagnetic tunnel junction (MTJ) structure 172 in between an optional seedlayer 118 and an optional cap layer 120. The MTJ structure 172 comprisesa magnetic free layer structure 122 and a magnetic reference layer 144with an insulating tunnel junction layer 126 interposed therebetween, ananti-ferromagnetic coupling layer 164 formed adjacent to the magneticreference layer 144, and a magnetic fixed layer 166 formed adjacent tothe anti-ferromagnetic coupling layer 164. The magnetic fixed layer 166and the magnetic free layer structure 122 may be formed adjacent to theoptional seed layer 118 and cap layer 120, respectively. The memoryelement 170 of FIG. 7A is different from the memory element 140 of FIG.4A in that the anti-ferromagnetic coupling layer 164 and the magneticfixed layer 166 have been inserted in between the optional seed layer118 and the magnetic reference layer 144.

The magnetic free layer structure 122 includes a first magnetic freelayer 128 formed adjacent to the insulating tunnel junction layer 126and a second magnetic free layer 130 separated from the first magneticfree layer 128 by a perpendicular enhancement layer (PEL) 132. The firstand the second magnetic free layers 128 and 130 have respectively firstand second variable magnetization directions 129 and 131 substantiallyperpendicular to the layer planes thereof. The first magnetic free layer128 may comprise one or more magnetic sublayers having the firstvariable magnetization direction 129. Likewise, the second magnetic freelayer 130 may comprise one or more magnetic sublayers having the secondvariable magnetization direction 131. The first and the second variablemagnetization directions 129 and 131 may be parallel or anti-parallel toeach other.

The magnetic reference layer 144 has a first fixed magnetizationdirection 145 substantially perpendicular to the layer plane thereof.The magnetic reference layer 144 may comprise one or more magneticsublayers having the first fixed magnetization direction 145.

The magnetic fixed layer 166 has a second fixed magnetization direction167 that is substantially perpendicular to the layer plane thereof andis substantially opposite to the first fixed magnetization direction145. The magnetic fixed layer 166 may comprise one or more magneticsublayers having the second fixed magnetization direction 167.

The stacking order of the individual layers in the MTJ structure 172 ofthe memory element 170 may be inverted as illustrated in FIG. 7B withoutaffecting the device performance. The memory element 170′ of FIG. 7B hasan MTJ structure 172′ that has the same layers but with the invertedstacking order comparing to the MTJ structure 172. Accordingly, themagnetic free layer structure 122 and the magnetic fixed layer 166 maybe formed adjacent to the optional seed layer 118 and cap layer 120,respectively.

A sixth embodiment of the present invention as applied to an MTJ memoryelement is illustrated in FIG. 8A. The memory element 180 includes amagnetic tunnel junction (MTJ) structure 182 in between an optional seedlayer 118 and an optional cap layer 120. The MTJ structure 182 comprisesa magnetic free layer 154 and a magnetic reference layer structure 124with an insulating tunnel junction layer 126 interposed therebetween, ananti-ferromagnetic coupling layer 164 formed adjacent to the magneticreference layer structure 124, and a magnetic fixed layer 166 formedadjacent to the anti-ferromagnetic coupling layer 164. The magneticfixed layer 166 and the magnetic free layer 154 may be formed adjacentto the optional seed layer 118 and cap layer 120, respectively. Thememory element 180 of FIG. 8A is different from the memory element 150of FIG. 5A in that the anti-ferromagnetic coupling layer 164 and themagnetic fixed layer 166 have been inserted in between the optional seedlayer 118 and the magnetic reference layer structure 124.

The magnetic free layer 154 has a variable magnetization direction 155substantially perpendicular to the layer plane thereof. The magneticfree layer 154 may comprise one or more magnetic sublayers having thevariable magnetization direction 155.

The magnetic reference layer structure 124 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by a perpendicular enhancement layer138. The first and second magnetic reference layers 134 and 136 have afirst fixed magnetization direction 125 substantially perpendicular tothe layer planes thereof. Each of the first magnetic reference layer 134and the second magnetic reference layer 136 may comprise one or moremagnetic sublayers having the first fixed magnetization direction 125.

The magnetic fixed layer 166 has a second fixed magnetization direction167 that is substantially perpendicular to the layer plane thereof andis substantially opposite to the first fixed magnetization direction125. The magnetic fixed layer 166 may comprise one or more magneticsublayers having the second fixed magnetization direction 167.

The stacking order of the individual layers in the MTJ structure 182 ofthe memory element 180 may be inverted as illustrated in FIG. 8B withoutaffecting the device performance. The memory element 180′ of FIG. 8B hasan MTJ structure 182′ that has the same layers but with the invertedstacking order comparing to the MTJ structure 182. Accordingly, themagnetic free layer 154 and the magnetic fixed layer 166 may be formedadjacent to the optional seed layer 118 and cap layer 120, respectively.

Comparing with the MTJ structures 116, 116′, 142, 142′, 152, and 152′ ofFIGS. 3A, 3B, 4A, 4B, 5A, and 5B, respectively, the MTJ structures 162,162′, 172, 172′, 182, and 182′ of FIGS. 6A, 6B, 7A, 7B, 8A, and 8B,respectively, have the magnetic fixed layer 166 anti-ferromagneticallycoupled to the magnetic reference layer structure 124 or the magneticreference layer 144 through the anti-ferromagnetic coupling layer 164.The magnetic fixed layer 166 is not an “active” layer like the magneticreference layer structure and the magnetic free layer structure, whichalong with the tunnel junction layer 126 collectively form an MTJ thatchanges resistivity when a spin-polarized current pass therethrough. Themagnetic fixed layer 166, which has an opposite magnetization directioncompared with the magnetic reference layer structure 124 and themagnetic reference layer 144, may pin or stabilize the magnetization ofthe magnetic reference layer structure 124 and the magnetic referencelayer 144 and may cancel, as much as possible, the external magneticfield exerted by the magnetic reference layer structure 124 or themagnetic reference layer 144 on the magnetic free layer structure 122 orthe magnetic free layer 154, thereby minimizing the offset field or netexternal field in the magnetic free layer structure 122 or the magneticfree layer 154.

A seventh embodiment of the present invention as applied to an MTJmemory element is illustrated in FIG. 9A. The memory element 190includes a magnetic tunnel junction (MTJ) structure 192 in between anoptional seed layer 118 and an optional cap layer 120. The MTJ structure192 comprises a magnetic free layer structure 122 and a magneticreference layer structure 124 with an insulating tunnel junction layer126 interposed therebetween, a tuning layer 194 formed adjacent to themagnetic free layer structure 122, and a magnetic compensation layer 196formed adjacent to the tuning layer 194. The magnetic reference layerstructure 124 and the magnetic compensation layer 196 may be formedadjacent to the optional seed layer 118 and cap layer 120, respectively.The memory element 190 of FIG. 9A is different from the memory element114 of FIG. 3A in that the tuning layer 194 and the magneticcompensation layer 196 have been inserted in between the magnetic freelayer structure 122 and the optional cap layer 120.

The magnetic free layer structure 122 includes a first magnetic freelayer 128 formed adjacent to the insulating tunnel junction layer 126and a second magnetic free layer 130 separated from the first magneticfree layer 128 by a first perpendicular enhancement layer (PEL) 132. Thefirst and the second magnetic free layers 128 and 130 have respectivelyfirst and second variable magnetization directions 129 and 131substantially perpendicular to the layer planes thereof. The firstmagnetic free layer 128 may comprise one or more magnetic sublayershaving the first variable magnetization direction 129. Likewise, thesecond magnetic free layer 130 may comprise one or more magneticsublayers having the second variable magnetization direction 131. Thefirst and the second variable magnetization directions 129 and 131 maybe parallel or anti-parallel to each other.

The magnetic reference layer structure 124 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by a second perpendicular enhancementlayer 138. The first and second magnetic reference layers 134 and 136have a first fixed magnetization direction 125 substantiallyperpendicular to the layer planes thereof. Each of the first magneticreference layer 134 and the second magnetic reference layer 136 maycomprise one or more magnetic sublayers having the first fixedmagnetization direction 125.

The magnetic compensation layer 196 has a third fixed magnetizationdirection 197 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first fixed magnetizationdirection 125. The magnetic compensation layer 196 may comprise one ormore magnetic sublayers having the third fixed magnetization direction197.

The stacking order of the individual layers in the MTJ structure 192 ofthe memory element 190 may be inverted as illustrated in FIG. 9B withoutaffecting the device performance. The memory element 190′ of FIG. 9B hasan MTJ structure 192′ that has the same layers but with the invertedstacking order comparing to the MTJ structure 192. Accordingly, themagnetic compensation layer 196 and the magnetic reference layerstructure 124 may be formed adjacent to the optional seed layer 118 andcap layer 120, respectively.

An eighth embodiment of the present invention as applied to an MTJmemory element is illustrated in FIG. 10A. The memory element 200includes a magnetic tunnel junction (MTJ) structure 202 in between anoptional seed layer 118 and an optional cap layer 120. The MTJ structure202 comprises a magnetic free layer structure 122 and a magneticreference layer 144 with an insulating tunnel junction layer 126interposed therebetween, a tuning layer 194 formed adjacent to themagnetic free layer structure 122, and a magnetic compensation layer 196formed adjacent to the tuning layer 194. The magnetic reference layer144 and the magnetic compensation layer 196 may be formed adjacent tothe optional seed layer 118 and cap layer 120, respectively. The memoryelement 200 of FIG. 10A is different from the memory element 140 of FIG.4A in that the tuning layer 194 and the magnetic compensation layer 196have been inserted in between the magnetic free layer structure 122 andthe optional cap layer 120.

The magnetic free layer structure 122 includes a first magnetic freelayer 128 formed adjacent to the insulating tunnel junction layer 126and a second magnetic free layer 130 separated from the first magneticfree layer 128 by a perpendicular enhancement layer (PEL) 132. The firstand the second magnetic free layers 128 and 130 have respectively firstand second variable magnetization directions 129 and 131 substantiallyperpendicular to the layer planes thereof. The first magnetic free layer128 may comprise one or more magnetic sublayers having the firstvariable magnetization direction 129. Likewise, the second magnetic freelayer 130 may comprise one or more magnetic sublayers having the secondvariable magnetization direction 131. The first and the second variablemagnetization directions 129 and 131 may be parallel or anti-parallel toeach other.

The magnetic reference layer 144 has a first fixed magnetizationdirection 145 substantially perpendicular to the layer plane thereof.The magnetic reference layer 144 may comprise one or more magneticsublayers having the first fixed magnetization direction 145.

The magnetic compensation layer 196 has a third fixed magnetizationdirection 197 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first fixed magnetizationdirection 145. The magnetic compensation layer 196 may comprise one ormore magnetic sublayers having the third fixed magnetization direction197.

The stacking order of the individual layers in the MTJ structure 202 ofthe memory element 200 may be inverted as illustrated in FIG. 10Bwithout affecting the device performance. The memory element 200′ ofFIG. 10B has an MTJ structure 202′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 202. Accordingly,the magnetic compensation layer 196 and the magnetic reference layer 144may be formed adjacent to the optional seed layer 118 and cap layer 120,respectively.

A ninth embodiment of the present invention as applied to an MTJ memoryelement is illustrated in FIG. 11A. The memory element 210 includes amagnetic tunnel junction (MTJ) structure 212 in between an optional seedlayer 118 and an optional cap layer 120. The MTJ structure 212 comprisesa magnetic free layer 154 and a magnetic reference layer structure 124with an insulating tunnel junction layer 126 interposed therebetween, atuning layer 194 formed adjacent to the magnetic free layer 154, and amagnetic compensation layer 196 formed adjacent to the tuning layer 194.The magnetic reference layer structure 124 and the magnetic compensationlayer 196 may be formed adjacent to the optional seed layer 118 and caplayer 120, respectively. The memory element 210 of FIG. 11A is differentfrom the memory element 150 of FIG. 5A in that the tuning layer 194 andthe magnetic compensation layer 196 have been inserted in between themagnetic free layer 154 and the optional cap layer 120.

The magnetic free layer 154 has a variable magnetization direction 155substantially perpendicular to the layer plane thereof. The magneticfree layer 154 may comprise one or more magnetic sublayers having thevariable magnetization direction 155.

The magnetic reference layer structure 124 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by a perpendicular enhancement layer138. The first and second magnetic reference layers 134 and 136 have afirst fixed magnetization direction 125 substantially perpendicular tothe layer planes thereof. Each of the first magnetic reference layer 134and the second magnetic reference layer 136 may comprise one or moremagnetic sublayers having the first fixed magnetization direction 125.

The magnetic compensation layer 196 has a third fixed magnetizationdirection 197 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first fixed magnetizationdirection 125. The magnetic compensation layer 196 may comprise one ormore magnetic sublayers having the third fixed magnetization direction197.

The stacking order of the individual layers in the MTJ structure 212 ofthe memory element 210 may be inverted as illustrated in FIG. 11Bwithout affecting the device performance. The memory element 210′ ofFIG. 11B has an MTJ structure 212′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 212. Accordingly,the magnetic compensation layer 196 and the magnetic reference layerstructure 124 may be formed adjacent to the optional seed layer 118 andcap layer 120, respectively.

Comparing with the MTJ structures 116, 116′, 142, 142′, 152, and 152′ ofFIGS. 3A/B-5A/B, respectively, the MTJ structures 192, 192′, 202, 202′,212, and 212′ of FIGS. 9A/B-11A/B, respectively, have the magneticcompensation layer 196 separated from the magnetic free layer structure122 or the magnetic free layer 154 by the tuning layer 194. Similar tothe magnetic fixed layer 166, the magnetic compensation layer 196 is notan “active” layer like the magnetic reference layer structure 124 andthe magnetic free layer structure 122, which along with the tunneljunction layer 126 collectively form an MTJ that changes resistivitywhen a spin-polarized current pass therethrough. One of the functions ofthe magnetic compensation layer 196, which has an opposite magnetizationdirection compared with the magnetic reference layer structure 124 andthe magnetic reference layer 144, is to cancel, as much as possible, theexternal magnetic field exerted by the magnetic reference layerstructure 124 or the magnetic reference layer 144 on the magnetic freelayer structures 122 or the magnetic free layer 154, thereby minimizingthe offset field or net external field in the magnetic free layerstructures 122 or the magnetic free layer 154. The strength of theexternal magnetic field exerted by the magnetic compensation layer 196on the magnetic free layer structure 122 or the magnetic free layer 154can be modulated by varying the thickness of the tuning layer 194, whichchanges the separation distance between the magnetic compensation layer196 and the magnetic free layer structure 122 or the magnetic free layer154.

The tuning layer 194 may also improve the perpendicular anisotropy ofthe magnetic layers formed adjacent thereto. The tuning layer 194 maycomprise one or more tuning sublayers, which may be formed adjacent toeach other.

A tenth embodiment of the present invention as applied to aperpendicular MTJ memory element is illustrated in FIG. 12A. The memoryelement 220 includes a magnetic tunnel junction (MTJ) structure 222 inbetween an optional seed layer 118 and an optional cap layer 120. TheMTJ structure 222 comprises a magnetic free layer structure 122 and amagnetic reference layer structure 124 with an insulating tunneljunction layer 126 interposed therebetween, a tuning layer 194 formedadjacent to the magnetic free layer structure 122 opposite theinsulating tunnel junction layer 126, a magnetic compensation layer 196formed adjacent to the tuning layer 194 opposite the magnetic free layerstructure 122, an anti-ferromagnetic coupling layer 164 formed adjacentto the magnetic reference layer structure 124 opposite the insulatingtunnel junction layer 126, and a magnetic fixed layer 166 formedadjacent to the anti-ferromagnetic coupling layer 164 opposite themagnetic reference layer structure 124. The magnetic fixed layer 166 andthe magnetic compensation layer 196 may be formed adjacent to theoptional seed layer 118 and cap layer 120, respectively. The memoryelement 220 of FIG. 12A is different from the memory element 190 of FIG.9A in that the magnetic fixed layer 166 and the anti-ferromagneticcoupling layer 164 have been inserted in between the magnetic referencelayer structure 124 and the optional seed layer 118.

The magnetic free layer structure 122 includes a first magnetic freelayer 128 formed adjacent to the insulating tunnel junction layer 126and a second magnetic free layer 130 separated from the first magneticfree layer 128 by a first perpendicular enhancement layer (PEL) 132. Thefirst and the second magnetic free layers 128 and 130 have respectivelyfirst and second variable magnetization directions 129 and 131substantially perpendicular to the layer planes thereof. The firstmagnetic free layer 128 may comprise one or more magnetic sublayershaving the first variable magnetization direction 129. Likewise, thesecond magnetic free layer 130 may comprise one or more magneticsublayers having the second variable magnetization direction 131. Thefirst and the second variable magnetization directions 129 and 131 maybe parallel or anti-parallel to each other.

The magnetic reference layer structure 124 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by a second perpendicular enhancementlayer 138. The first and second magnetic reference layers 134 and 136have a first fixed magnetization direction 125 substantiallyperpendicular to the layer planes thereof. Each of the first magneticreference layer 134 and the second magnetic reference layer 136 maycomprise one or more magnetic sublayers having the first fixedmagnetization direction 125.

The magnetic compensation layer 196 has a third fixed magnetizationdirection 197 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first fixed magnetizationdirection 125. The magnetic compensation layer 196 may comprise one ormore magnetic sublayers having the third fixed magnetization direction197.

The magnetic fixed layer 166 has a second fixed magnetization direction167 that is substantially perpendicular to the layer plane thereof andis substantially opposite to the first fixed magnetization direction125. The magnetic fixed layer 166 may comprise one or more magneticsublayers having the second fixed magnetization direction 167.

The stacking order of the individual layers in the MTJ structure 222 ofthe memory element 220 may be inverted as illustrated in FIG. 12Bwithout affecting the device performance. The memory element 220′ ofFIG. 12B has an MTJ structure 222′ that has the same layers but with theinverted stacking order comparing with the MTJ structure 222.Accordingly, the magnetic compensation layer 196 and the magnetic fixedlayer 166 may be formed adjacent to the optional seed layer 118 and caplayer 120, respectively.

An eleventh embodiment of the present invention as applied to aperpendicular MTJ memory element is illustrated in FIG. 13A. The memoryelement 224 includes a magnetic tunnel junction (MTJ) structure 226 inbetween an optional seed layer 118 and an optional cap layer 120. TheMTJ structure 226 comprises a magnetic free layer structure 122 and amagnetic reference layer 144 with an insulating tunnel junction layer126 interposed therebetween, a tuning layer 194 formed adjacent to themagnetic free layer structure 122 opposite the insulating tunneljunction layer 126, a magnetic compensation layer 196 formed adjacent tothe tuning layer 194 opposite the magnetic free layer structure 122, ananti-ferromagnetic coupling layer 164 formed adjacent to the magneticreference layer 144 opposite the insulating tunnel junction layer 126,and a magnetic fixed layer 166 formed adjacent to the anti-ferromagneticcoupling layer 164 opposite the magnetic reference layer 144. Themagnetic fixed layer 166 and the magnetic compensation layer 196 may beformed adjacent to the optional seed layer 118 and cap layer 120,respectively. The memory element 224 of FIG. 13A is different from thememory element 200 of FIG. 10A in that the magnetic fixed layer 166 andthe anti-ferromagnetic coupling layer 164 have been inserted in betweenthe magnetic reference layer 144 and the optional seed layer 118.

The magnetic free layer structure 122 includes a first magnetic freelayer 128 formed adjacent to the insulating tunnel junction layer 126and a second magnetic free layer 130 separated from the first magneticfree layer 128 by a perpendicular enhancement layer (PEL) 132. The firstand the second magnetic free layers 128 and 130 have respectively firstand second variable magnetization directions 129 and 131 substantiallyperpendicular to the layer planes thereof. The first magnetic free layer128 may comprise one or more magnetic sublayers having the firstvariable magnetization direction 129. Likewise, the second magnetic freelayer 130 may comprise one or more magnetic sublayers having the secondvariable magnetization direction 131. The first and the second variablemagnetization directions 129 and 131 may be parallel or anti-parallel toeach other.

The magnetic reference layer 144 has a first fixed magnetizationdirection 145 substantially perpendicular to the layer plane thereof.The magnetic reference layer 144 may comprise one or more magneticsublayers having the first fixed magnetization direction 145.

The magnetic compensation layer 196 has a third fixed magnetizationdirection 197 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first fixed magnetizationdirection 145. The magnetic compensation layer 196 may comprise one ormore magnetic sublayers having the third fixed magnetization direction197.

The magnetic fixed layer 166 has a second fixed magnetization direction167 that is substantially perpendicular to the layer plane thereof andis substantially opposite to the first fixed magnetization direction145. The magnetic fixed layer 166 may comprise one or more magneticsublayers having the second fixed magnetization direction 167.

The stacking order of the individual layers in the MTJ structure 226 ofthe memory element 224 may be inverted as illustrated in FIG. 13Bwithout affecting the device performance. The memory element 224′ ofFIG. 13B has an MTJ structure 226′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 226. Accordingly,the magnetic compensation layer 196 and the magnetic fixed layer 166 maybe formed adjacent to the optional seed layer 118 and cap layer 120,respectively.

A twelfth embodiment of the present invention as applied to aperpendicular MTJ memory element is illustrated in FIG. 14A. The memoryelement 228 includes a magnetic tunnel junction (MTJ) structure 229 inbetween an optional seed layer 118 and an optional cap layer 120. TheMTJ structure 229 comprises a magnetic free layer 154 and a magneticreference layer structure 124 with an insulating tunnel junction layer126 interposed therebetween, a tuning layer 194 formed adjacent to themagnetic free layer 154 opposite the insulating tunnel junction layer126, a magnetic compensation layer 196 formed adjacent to the tuninglayer 194 opposite the magnetic free layer 154, an anti-ferromagneticcoupling layer 164 formed adjacent to the magnetic reference layerstructure 124 opposite the insulating tunnel junction layer 126, and amagnetic fixed layer 166 formed adjacent to the anti-ferromagneticcoupling layer 164 opposite the magnetic reference layer structure 124.The magnetic fixed layer 166 and the magnetic compensation layer 196 maybe formed adjacent to the optional seed layer 118 and cap layer 120,respectively. The memory element 228 of FIG. 14A is different from thememory element 210 of FIG. 11A in that the magnetic fixed layer 166 andthe anti-ferromagnetic coupling layer 164 have been inserted in betweenthe magnetic reference layer structure 124 and the optional seed layer118.

The magnetic free layer 154 has a variable magnetization direction 155substantially perpendicular to the layer plane thereof. The magneticfree layer 154 may comprise one or more magnetic sublayers having thevariable magnetization direction 155.

The magnetic reference layer structure 124 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by a perpendicular enhancement layer138. The first and second magnetic reference layers 134 and 136 have afirst fixed magnetization direction 125 substantially perpendicular tothe layer planes thereof. Each of the first magnetic reference layer 134and the second magnetic reference layer 136 may comprise one or moremagnetic sublayers having the first fixed magnetization direction 125.

The magnetic compensation layer 196 has a third fixed magnetizationdirection 197 that is substantially perpendicular to the layer planethereof and is substantially opposite to the first fixed magnetizationdirection 125. The magnetic compensation layer 196 may comprise one ormore magnetic sublayers having the third fixed magnetization direction197.

The magnetic fixed layer 166 has a second fixed magnetization direction167 that is substantially perpendicular to the layer plane thereof andis substantially opposite to the first fixed magnetization direction125. The magnetic fixed layer 166 may comprise one or more magneticsublayers having the second fixed magnetization direction 167.

The stacking order of the individual layers in the MTJ structure 229 ofthe memory element 228 may be inverted as illustrated in FIG. 14Bwithout affecting the device performance. The memory element 228′ ofFIG. 14B has an MTJ structure 229′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 229. Accordingly,the magnetic compensation layer 196 and the magnetic fixed layer 166 maybe formed adjacent to the optional seed layer 118 and cap layer 120,respectively.

The magnetic free layers 128, 130, and 154, the magnetic referencelayers 134, 136, and 144, the magnetic fixed layer 166, and the magneticcompensation layer 196 of above embodiments may be made of any suitablemagnetic material or structure. One or more of the magnetic layers 128,130, 134, 136, 144, 154, 166, and 196 may comprise at least oneferromagnetic element, such as but not limited to cobalt (Co), nickel(Ni), or iron (Fe), to form a suitable magnetic material, such as butnot limited to Co, Ni, Fe, CoNi, CoFe, NiFe, or CoNiFe. The magneticmaterial of the one or more of the magnetic layers 128, 130, 134, 136,144, 154, 166, and 196 may further include one or more non-magneticelements, such as but not limited to boron (B), titanium (Ti), zirconium(Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium(Cr), molybdenum (Mo), tungsten (W), aluminum (Al), silicon (Si),germanium (Ge), gallium (Ga), oxygen (O), nitrogen (N), carbon (C),platinum (Pt), palladium (Pd), ruthenium (Ru), samarium (Sm), neodymium(Nd), or phosphorus (P), to form a magnetic alloy or compound, such asbut not limited to cobalt-iron-boron (CoFeB), iron-platinum (FePt),cobalt-platinum (CoPt), cobalt-platinum-chromium (CoPtCr),cobalt-iron-boron-titanium (CoFeBTi), cobalt-iron-boron-zirconium,(CoFeBZr), cobalt-iron-boron-hafnium (CoFeBHf),cobalt-iron-boron-vanadium (CoFeBV), cobalt-iron-boron-tantalum(CoFeBTa), cobalt-iron-boron-chromium (CoFeBCr), cobalt-iron-titanium(CoFeTi), cobalt-iron-zirconium (CoFeZr), cobalt-iron-hafnium (CoFeHf),cobalt-iron-vanadium (CoFeV), cobalt-iron-niobium (CoFeNb),cobalt-iron-tantalum (CoFeTa), cobalt-iron-chromium (CoFeCr),cobalt-iron-molybdenum (CoFeMo), cobalt-iron-tungsten (CoFeW),cobalt-iron-aluminum (CoFeAl), cobalt-iron-silicon (CoFeSi),cobalt-iron-germanium (CoFeGe), iron-zirconium-boron (FeZrB),samarium-cobalt (SmCo), neodymium-iron-boron (NdFeB), orcobalt-iron-phosphorous (CoFeP).

Some of the above-mentioned magnetic materials, such as Fe, CoFe, CoFeBmay have a body-centered cubic (BCC) lattice structure that iscompatible with the halite-like cubic lattice structure of MgO, whichmay be used as the insulating tunnel junction layer 126. CoFeB alloyused for one or more of the magnetic layers 128, 130, 134, 136, 144,154, 166, and 196 may contain more than 40 atomic percent Fe or maycontain less than 30 atomic percent B or both.

The first magnetic reference layer 134 may be made of a magneticmaterial comprising Co, Fe, and B with a thickness in the range of about0.6 nm to about 1.8 nm, while the second magnetic reference layer 136may be made of a material comprising Co, Fe, and B with a thickness inthe range of about 0.6 nm to about 2.0 nm.

One or more of the magnetic layers 128, 130, 134, 136, 144, 154, 166,and 196 may alternatively have a multilayer structure formed byinterleaving layers of a first type of material with layers of a secondtype of material with at least one of the two types of materials beingmagnetic, such as but not limited to [Co/Pt], [Co/Pd], [Co/Pt(Pd)],[Co/Ni], [CoFe/Pt], [CoFe/Pd], [CoFe/Pt(Pd)], [CoFe/Ni], or anycombination thereof. The multilayer structure may have a face-centeredcubic (FCC) type of lattice structure, which is different from thebody-centered cubic structure (BCC) of some ferromagnetic materials,such as Fe, CoFe, and CoFeB, and the halite-like cubic lattice structureof magnesium oxide (MgO) that may be used as the insulating tunneljunction layer 126. All individual magnetic layers of a magneticmultilayer structure may have the same magnetization direction. Themultilayer structure may or may not exhibit the characteristic satellitepeaks associated with superlattice when analyzed by X-ray, neutrondiffraction, or other diffraction techniques.

Still alternatively, one or more of the magnetic layers 128, 130, 134,136, 144, 154, 166, and 196 may comprise two, three, four, or moremagnetic sublayers with each magnetic sublayer being made of anysuitable magnetic material, including magnetic metal, alloy, compound,or multilayer structure, as described in the preceding paragraphs above.The magnetic sublayers of a magnetic layer may form adjacent to eachother and may have the same magnetization direction. For example, themagnetic reference layer 144 of the embodiments of FIGS. 4A, 4B, 7A, 7B,10A, 10B, 13A, and 13B may further comprise three magnetic sublayers.FIGS. 15A and 15B illustrate the magnetic reference layer 144 of theembodiments of FIGS. 7A and 7B comprising a first magnetic referencesublayer 234 formed adjacent to the insulating tunnel junction layer 126and a second magnetic reference sublayer 236 separated from the firstmagnetic reference sublayer 234 by an intermediate magnetic referencesublayer 266. Each of the first, second, and intermediate magneticreference sublayers 234, 236, and 266 may be made of any suitablemagnetic material or structure as described above. The first, second,and intermediate magnetic reference sublayers 234, 236, and 266 have thefirst fixed magnetization direction 145 substantially perpendicular tothe layer planes thereof. Alternatively, the magnetic reference layer144 of the embodiments of FIGS. 4A, 4B, 7A, 7B, 10A, 10B, 13A, and 13Bmay include two, four, or more magnetic sublayers, which may formadjacent to each other and may have the same magnetization direction.

The second magnetic free layer 130 of the embodiments of FIGS. 3A, 3B,4A, 4B, 6A, 6B, 7A, 7B, 9A, 9B, 10A, 10B, 12A, 12B, 13A, and 13B mayfurther comprise a first magnetic free sublayer 280 formed adjacent tothe perpendicular enhancement layer (PEL) 132 and a second magnetic freesublayer 282 formed adjacent to the first magnetic free sublayer 280opposite the PEL 132 as illustrated in FIGS. 16A and 16B. Each of thefirst and second magnetic free sublayers 280 and 282 may be made of anysuitable magnetic material or structure as described above. The firstand second magnetic free sublayers 280 and 282 have the second variablemagnetization direction 131. Alternatively, the second magnetic freelayer 130 of the embodiments of FIGS. 3A, 3B, 4A, 4B, 6A, 6B, 7A, 7B,9A, 9B, 10A, 10B, 12A, 12B, 13A, and 13B may include three, four, ormore magnetic sublayers, which may form adjacent to each other and havethe same magnetization direction.

Similarly, the second magnetic reference layer 136 of the embodiments ofFIGS. 3A, 3B, 5A, 5B, 6A, 6B, 8A, 8B, 9A, 9B, 11A, 11B, 12A, 12B, 14Aand 14B may further comprise a first magnetic reference sublayer 274formed adjacent to the perpendicular enhancement layer 138 and a secondmagnetic reference sublayer 276 separated from the first magneticreference sublayer 274 by an intermediate reference sublayer 278 asillustrated in FIGS. 17A and 17B. The first and second magneticreference sublayers 274 and 276 have the first fixed magnetizationdirection 125. The first and second magnetic reference sublayers 274 and276 each may be made of any suitable magnetic material or structure asdescribed above, such as but not limited to Co or CoFe, and may have athickness in the range of about 0.2 nm to about 1.2 nm. The intermediatereference sublayer 278 may be made of palladium, platinum, or nickel andmay have a thickness in the range of about 0.2 nm to about 1.2 nm.Alternatively, the second magnetic reference layer 136 of theembodiments of FIGS. 3A, 3B, 5A, 5B, 6A, 6B, 8A, 8B, 9A, 9B, 11A, 11B,12A, 12B, 14A and 14B may include two or more magnetic sublayers, whichmay form adjacent to each other and have the same magnetizationdirection.

FIGS. 18A and 18B illustrate exemplary structures directed to theembodiments of FIGS. 6A, 6B, 8A, 8B, 12A, 12B, 14A, and 14B in which thesecond magnetic reference layer 136 comprises a first magnetic referencesublayer 290 formed adjacent to the PEL 138 and a second magneticreference sublayer 292 formed adjacent to the anti-ferromagneticcoupling layer 164. The first and second magnetic reference sublayers290 and 292 have the first fixed magnetization direction 125. Themagnetic fixed layer 166 in the exemplary structures of FIGS. 18A and18B may also comprise a second magnetic fixed sublayer 294 formedadjacent to the anti-ferromagnetic coupling layer 164 and a firstmagnetic fixed sublayer 296 formed adjacent to the second magnetic fixedsublayer 294. The first and second magnetic fixed sublayers 296 and 294have the second fixed magnetization direction 167 that is substantiallyopposite to the first fixed magnetization direction 125. One or more ofthe magnetic sublayers 290-296 may be made of any suitable magneticmaterial or structure as described above. At least one of the firstmagnetic reference sublayer 290, the second magnetic reference sublayer292, the first magnetic fixed sublayer 296, and the second magneticfixed sublayer 294 may have a multilayer structure, such as but notlimited to [Co/Pt], [Co/Pd], [Co/Pt(Pd)], [Co/Ni], [CoFe/Pt], [CoFe/Pd],[CoFe/Pt(Pd)], [CoFe/Ni], or any combination thereof.

In addition to the examples described above, one or more of the magneticfree layer 154, the first magnetic free layer 128, the first magneticreference layer 134, and the magnetic compensation layer 196 may alsocomprise two, three, four, or more magnetic sublayers with each magneticsublayer being made of any suitable magnetic material, includingmagnetic metal, alloy, compound, or multilayer structure, as describedabove. The individual magnetic sublayers of a magnetic layer may formadjacent to each other and may have the same magnetization direction.

The magnetic fixed layer 166 of the embodiments of FIGS. 6A/B-8A/B,12A/B-15A/B, and 18A/B may include two or more magnetic sublayers with aperpendicular enhancement layer interposed therebetween. FIGS. 19A and19B illustrate exemplary structures directed to the embodiment of FIGS.8A and 8B in which the magnetic fixed layer 166 includes the secondmagnetic fixed sublayer 294 formed adjacent to the anti-ferromagneticcoupling layer 164 and the first magnetic fixed sublayer 296 separatedfrom the second magnetic fixed sublayer 294 by a perpendicularenhancement layer 298. The first and second magnetic fixed sublayers 296and 294 have the second fixed magnetization direction 167 that issubstantially perpendicular to layer planes thereof and is substantiallyopposite to the first fixed magnetization direction 125. One or more ofthe magnetic fixed sublayers 294 and 296 may be made of any suitablemagnetic material or structure as described above. At least one of thefirst and second magnetic fixed sublayers 294 and 296 may have amultilayer structure, such as but not limited to [Co/Pt], [Co/Pd],[Co/Pt(Pd)], [Co/Ni], [CoFe/Pt], [CoFe/Pd], [CoFe/Pt(Pd)], [CoFe/Ni], orany combination thereof.

Alternatively, the magnetic reference layer structure 124 of theexemplary structures of FIGS. 19A and 19B may include the first andsecond magnetic reference layers 134 and 136 without the perpendicularenhancement layer 138 in between, resulting in a thirteenth embodimentas illustrated in FIGS. 20A and 20B. A memory element 300 of FIG. 20Aincludes a magnetic tunnel junction (MTJ) structure 302 in between theoptional seed layer 118 and the optional cap layer 120. The MTJstructure 302 comprises the magnetic free layer 154, the insulatingtunnel junction layer 126 formed adjacent thereto, the first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 opposite the magnetic free layer 154, the second magneticreference layer 136 formed adjacent to the first magnetic referencelayer 134, the anti-ferromagnetic coupling layer 164 formed adjacent tothe second magnetic reference layer 136, and the magnetic fixed layer166 formed adjacent to the anti-ferromagnetic coupling layer 164. Themagnetic fixed layer 166 and the magnetic free layer 154 may be formedadjacent to the optional seed layer 118 and cap layer 120, respectively.Like the exemplary structures of FIGS. 19A and 19B, the magnetic fixedlayer 166 of the memory element 300 includes the second magnetic fixedsublayer 294 formed adjacent to the anti-ferromagnetic coupling layer164 and the first magnetic fixed sublayer 296 separated from the secondmagnetic fixed sublayer 294 by the perpendicular enhancement layer 298.

The magnetic free layer 154 has a variable magnetization direction 155substantially perpendicular to the layer plane thereof. The magneticfree layer 154 may comprise one or more magnetic free sublayers havingthe variable magnetization direction 155. The magnetic free layer 154and the magnetic sublayers thereof, if any, may be made of any suitablemagnetic material, including magnetic metal, alloy, compound, ormultilayer structure, as described above.

The first and second magnetic reference layers 134 and 136 have a firstfixed magnetization direction 125 substantially perpendicular to thelayer planes thereof. Each of the first magnetic reference layer 134 andthe second magnetic reference layer 136 may comprise one or moremagnetic sublayers having the first fixed magnetization direction 125.The first and second magnetic reference layers 134 and 136 and themagnetic sublayers thereof, if any, may be made of any suitable magneticmaterial, including magnetic metal, alloy, compound, or multilayerstructure, as described above.

The first and second magnetic fixed sublayers 296 and 294 have thesecond fixed magnetization direction 167 that is substantiallyperpendicular to the layer planes thereof and is substantially oppositeto the first fixed magnetization direction 125. One or more of themagnetic fixed sublayers 294 and 296 may be made of any suitablemagnetic material, including magnetic metal, alloy, compound, ormultilayer structure, as described above. At least one of the first andsecond magnetic fixed sublayers 294 and 296 may have a multilayerstructure, such as but not limited to [Co/Pt], [Co/Pd], [Co/Pt(Pd)],[Co/Ni], [CoFe/Pt], [CoFe/Pd], [CoFe/Pt(Pd)], [CoFe/Ni], or anycombination thereof.

The stacking order of the individual layers in the MTJ structure 302 ofthe memory element 300 may be inverted as illustrated in FIG. 20Bwithout affecting the device performance. The memory element 300′ ofFIG. 20B has an MTJ structure 302′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 302. Accordingly,the magnetic free layer 154 and the magnetic fixed layer 166 may beformed adjacent to the optional seed layer 118 and cap layer 120,respectively.

The second magnetic free layer 130 of the embodiments of FIGS. 3A, 3B,4A, 4B, 6A, 6B, 7A, 7B, 9A, 9B, 10A, 10B, 12A, 12B, 13A, and 13B maycomprise one or more ferromagnetic elements and may have a layerthickness of less than about 2 nm, preferably less than about 1.5 nm,more preferably less than about 1 nm, even more preferably less thanabout 0.8 nm, still even more preferably between about 0.7 nm and about0.1 nm. At a thickness of less than about 1.5 nm, the second magneticfree layer 130 may become superparamagnetic or magnetically dead byexhibiting no net magnetic moment in the absence of an external magneticfield. The second magnetic free layer 130 may have any suitablecomposition that comprises one or more of the following materials: Co,Ni, Fe, CoNi, CoFe, NiFe, CoNiFe, CoFeB, B, Ti, Zr, Hf, V, Nb, Ta, Cr,Mo, W, Al, Si, Ge, Ga, O, N, C, Pt, Pd, Ru, Sm, Nd, and P.Alternatively, the second magnetic free layer 130 may have a nominalcomposition in which all ferromagnetic elements collectively account forless than about 80 at. %, preferably less than about 60 at. %, morepreferably less than about 50 at. %, even more preferably less thanabout 40 at. %. The second magnetic free layer 130 may becomenon-magnetic if the total content of the ferromagnetic elements is belowa certain threshold.

The insulating tunnel junction layer 126 for all perpendicular MTJstructures of FIGS. 3A/B-20A/B may be formed of a suitable insulatingmaterial containing oxygen, nitrogen, or both, such as but not limitedto magnesium oxide (MgO), aluminum oxide (AlO_(x)), titanium oxide(TiO_(x)), zirconium oxide (ZrO_(x)), hafnium oxide (HfO_(x)), vanadiumoxide (VO_(x)), tantalum oxide (TaO_(x)), chromium oxide (CrO_(x)),molybdenum oxide (MoO_(x)), tungsten oxide (WO_(x)), silicon oxide(SiO_(x)), silicon nitride (SiN_(x)), or any combination thereof. Theinsulating tunnel junction layer 126 may have a halite-like cubiclattice structure.

The anti-ferromagnetic coupling layer 164, which anti-ferromagneticallycouples the magnetic fixed layer 166 to the magnetic reference layers136 and 144 in the MTJ structures of FIGS. 6A/B-8A/B, 12A/B-15A/B, and18A/B-20A/B, may have a single layer structure or may comprise two,three, four, or more sublayers formed adjacent to each other. One ormore of the single layer and the multiple sublayers of theanti-ferromagnetic coupling layer 164 may be made of a suitableanti-ferromagnetic coupling material, such as but not limited toruthenium (Ru), vanadium (V), niobium (Nb), tantalum (Ta), chromium(Cr), molybdenum (Mo), tungsten (W), manganese (Mn), rhenium (Re),osmium (Os), rhodium (Rh), iridium (Ir), copper (Cu), or any combinationthereof.

In cases where one or more of the magnetic fixed layer 166 and themagnetic reference layers 136 and 144 comprise a multilayer structure inwhich one of the two interleaving material is non-magnetic, such as butnot limited to [Co/Pt], [Co/Pd], [Co/Pt(Pd)], [CoFe/Pt], [CoFe/Pd], or[CoFe/Pt(Pd)], an interface multilayer structure in which both of thetwo interleaving materials are magnetic, such as but not limited to[Co/Ni] or [CoFe/Ni], may be inserted between the multilayer structureand the anti-ferromagnetic coupling layer 164, thereby improving theanti-ferromagnetic coupling between the magnetic fixed layer 166 and themagnetic reference layers 136 and 144. For example, in the structures ofFIGS. 18A/B, the first magnetic reference sublayer 290 and the firstmagnetic fixed sublayer 296 each may have a multilayer structure, suchas but not limited to [Co/Pt], [Co/Pd], [Co/Pt(Pd)], [CoFe/Pt],[CoFe/Pd], [CoFe/Pt(Pd)], or any combination thereof. Accordingly, thesecond magnetic reference sublayer 292 and the second magnetic fixedsublayer 294 each may have a multilayer structure in which both of thetwo interleaving materials are magnetic, such as but not limited to[Co/Ni] or [CoFe/Ni], for improving the anti-ferromagnetic couplingbetween the magnetic fixed layer 166 and the magnetic reference layer136.

At least one of the perpendicular enhancement layers (PELs) 132, 138,and 298 formed in the magnetic free layer structure 122, the magneticreference layer structure 124, and the magnetic fixed layer 166,respectively, may have a single layer structure or may comprise two,three, four, or more perpendicular enhancement sublayers formed adjacentto each other. One or more of the single layer and the multiplesublayers of the PELs 132, 138, and 298 may have a thickness less thanabout 3 nm, preferably less than about 2 nm, more preferably less thanabout 1 nm, even more preferably less than about 0.8 nm, still even morepreferably less than about 0.6 nm. One or more of the single layer andthe multiple sublayers of the PELs 132, 138, and 298 may comprise one ormore of the following chemical elements: B, Mg, Ti, Zr, Hf, V, Nb, Ta,Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Al,Si, Ge, Ga, O, N, and C, thereby forming a suitable perpendicularenhancement material, such as but not limited to B, Mg, Ti, Zr, Hf, V,Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag,Au, Al, Si, Ge, Ga, MgO, TiO_(x), ZrO_(x), HfO_(x), VO_(x), NbO_(x),TaO_(x), CrO_(x), MoO_(x), WO_(x), RhO_(x), NiO_(x), PdO_(x), PtO_(x),CuO_(x), AgO_(x), RuO_(x), SiO_(x), TiN_(x), ZrN_(x), HfN_(x), VN_(x),NbN_(x), TaN_(x), CrN_(x), MoN_(x), WN_(x), NiN_(x), PdN_(x), PtO_(x),RuN_(x), SiN_(x), TiO_(x)N_(y), ZrO_(x)N_(y), HfO_(x)N_(y), VO_(x)N_(y),NbO_(x)N_(y), TaO_(x)N_(y), CrO_(x)N_(y), MoO_(x)N_(y), WO_(x)N_(y),NiO_(x)N_(y), PdO_(x)N_(y), PtO_(x)N_(y), RuO_(x)N_(y), SiO_(x)N_(y),TiRuO_(x), ZrRuO_(x), HfRuO_(x), VRuO_(x), NbRuO_(x), TaRuO_(x),CrRuO_(x), MoRuO_(x), WRuO_(x), RhRuO_(x), NiRuO_(x), PdRuO_(x),PtRuO_(x), CuRuO_(x), AgRuO_(x), CoFeB, CoFe, NiFe, CoFeNi, CoTi, CoZr,CoHf, CoV, CoNb, CoTa, CoFeTa, CoCr, CoMo, CoW, NiCr, NiTi, NiZr, NiHf,NiV, NiNb, NiTa, NiMo, NiW, CoNiTa, CoNiCr, CoNiTi, FeTi, FeZr, FeHf,FeV, FeNb, FeTa, FeCr, FeMo, FeW or any combination thereof. In caseswhere the perpendicular enhancement material contains one or moreferromagnetic elements, such as Co, Fe, and Ni, the total content of theferromagnetic elements of the perpendicular enhancement material may beless than the threshold required for becoming magnetic, therebyrendering the material essentially non-magnetic. Alternatively, theperpendicular enhancement material that contains one or moreferromagnetic elements may be very thin, thereby rendering the materialparamagnetic or magnetically dead. For example, the PEL 132, 138, or 298may be made of a single layer of Ta, Hf, or MgO, or a bilayer structurewith a Ta sublayer and a Hf sublayer formed adjacent to each other.

The optional seed layer 118 of the embodiments of FIGS. 3A/B-14A/B and19A/B-20A/B may have a single layer structure or may comprise two,three, four, or more sublayers formed adjacent to each other. One ormore of the single layer and the multiple sublayers of the seed layer118 may have a thickness less than about 3 nm, preferably less thanabout 2 nm, more preferably less than about 1 nm, even more preferablyless than about 0.8 nm, still even more preferably less than about 0.6nm. One or more of the single layer and the multiple sublayers of theseed layer 118 may comprise one or more of the following chemicalelements: B, Mg, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os,Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Al, Si, Ge, Ga, O, N, and C, therebyforming a suitable seed material such as one of those discussed abovefor the perpendicular enhancement material. For example, the seed layer118 may be made of a single layer of MgO, Ta, Hf, W, Mo, Ru, Pt, Pd,NiCr, NiTa, NiTi, or TaN_(x). Alternatively, the seed layer 118 may havea bilayer structure (Ru/Ta) comprising a Ta sublayer formed adjacent toone of the magnetic layers 144, 154, 166, and 196 or structures 122 and124 and a Ru sublayer formed beneath the Ta sublayer. Other exemplarybilayer structures (bottom/top), such as Ta/Ru, Ta/Hf, Hf/Ta, Ta/W,W/Ta, Ru/W, W/Ru, MgO/Ta, Ta/MgO, Ru/MgO, Hf/MgO, and W/MgO, may also beused for the seed layer 118. Still alternatively, the seed layer 118 mayhave a bilayer structure comprising an oxide sublayer, such as MgO,formed adjacent to one of the magnetic layers 144, 154, 166, and 196 orstructures 122 and 124 and an underlying, thin conductive sublayer, suchas CoFeB which may be non-magnetic or amorphous or both. Additional seedsublayers may further form beneath the exemplary CoFeB/MgO seed layer toform other seed layer structures, such as but not limited toRu/CoFeB/MgO, Ta/CoFeB/MgO, W/CoFeB/MgO, Hf/CoFeB/MgO, Ta/Ru/CoFeB/MgO,Ru/Ta/CoFeB/MgO, W/Ta/CoFeB/MgO, Ta/W/CoFeB/MgO, W/Ru/CoFeB/MgO,Ru/W/CoFeB/MgO, Hf/Ta/CoFeB/MgO, Ta/Hf/CoFeB/MgO, W/Hf/CoFeB/MgO,Hf/W/CoFeB/MgO, Hf/Ru/CoFeB/MgO, Ru/Hf/CoFeB/MgO, Ta/W/Ru/CoFeB/MgO,Ta/Ru/W/CoFeB/MgO, and Ru/Ta/Ru/CoFeB/MgO. Still alternatively, the seedlayer 118 may have a multilayer structure formed by interleaving seedsublayers of a first type with seed sublayers of a second type. One orboth types of the seed sublayers may comprise one or more ferromagneticelements, such as Co, Fe, and Ni. One or both types of seed sublayersmay be amorphous or noncrystalline. For example, the first and secondtypes of sublayers may be made of Ta and CoFeB, both of which may beamorphous. Moreover, one of the Ta sublayers may be formed adjacent tothe one of the magnetic layers 144, 154, 166, and 196 or structures 122and 124 and the CoFeB sublayers may be non-magnetic orsuperparamagnetic.

The optional cap layer 120 of the embodiments of FIGS. 3A/B-14A/B and19A/B-20A/B may have a single layer structure or may comprise two,three, four, or more sublayers formed adjacent to each other. One ormore of the single layer and the multiple sublayers of the cap layer 120may have a thickness less than about 3 nm, preferably less than about 2nm, more preferably less than about 1 nm, even more preferably less thanabout 0.8 nm, still even more preferably less than about 0.6 nm. One ormore of the single layer and the multiple sublayers of the cap layer 120may comprise one or more of the following chemical elements: B, Mg, Ti,Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd,Pt, Cu, Ag, Au, Al, Si, Ge, Ga, O, N, and C, thereby forming a suitablecap material such as one of those discussed above for the perpendicularenhancement material. For example, the cap layer 120 may be made of asingle layer of MgO, Ta, Hf, W, Mo, Ru, Pt, or Pd. Alternatively, thecap layer 120 may have a bilayer structure (W/Ta) comprising a Wsublayer formed adjacent to one of the magnetic layers 144, 154, 166,and 196 or structures 122 and 124 and a Ta sublayer formed on top of theW sublayer. Other exemplary bilayer structures (bottom/top), such asTa/Ru, Ru/Ta, Ta/Hf, Hf/Ta, Ta/W, Ru/W, W/Ru, MgO/Ta, Ta/MgO, MgO/Ru,MgO/Hf, and MgO/W, may also be used for the cap layer 120. Stillalternatively, the cap layer 120 may have a bilayer structure comprisingan oxide sublayer, such as MgO, formed adjacent to one of the magneticlayers 144, 154, 166, and 196 or structures 122 and 124 and a thinconductive sublayer, such as CoFeB which may be non-magnetic orsuperparamagnetic. Additional cap sublayers may further form on top ofthe exemplary MgO/CoFeB cap layer to form other cap layer structures,such as but not limited to MgO/CoFeB/Ru, MgO/CoFeB/Ta, MgO/CoFeB/W,MgO/CoFeB/Hf, MgO/CoFeB/Ru/Ta, MgO/CoFeB/Ta/Ru, MgO/CoFeB/W/Ta,MgO/CoFeB/Ta/W, MgO/CoFeB/W/Ru, MgO/CoFeB/Ru/W, MgO/CoFeB/Hf/Ta,MgO/CoFeB/Ta/Hf, MgO/CoFeB/Hf/W, MgO/CoFeB/W/Hf, MgO/CoFeB/Hf/Ru,MgO/CoFeB/Ru/Hf, MgO/CoFeB/Ru/W/Ta, MgO/CoFeB/W/Ru/Ta, andMgO/CoFeB/Ru/Ta/Ru. As such, the cap layer 120 may comprise aninsulating cap sublayer and one or more conductive cap sublayers formedthereon.

The tuning layer 194 of the embodiments of FIGS. 9A/B-14A/B may have asingle layer structure or may comprise two, three, four, or moresublayers formed adjacent to each other. One or more of the single layerand the multiple sublayers of the tuning layer 194 may have a thicknessless than about 3 nm, preferably less than about 2 nm, more preferablyless than about 1 nm, even more preferably less than about 0.8 nm, stilleven more preferably less than about 0.6 nm. One or more of the singlelayer and the multiple sublayers of the tuning layer 194 may compriseone or more of the following chemical elements: B, Mg, Ti, Zr, Hf, V,Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag,Au, Al, Si, Ge, Ga, O, N, and C, thereby forming a suitable tuningmaterial such as one of those discussed above for the perpendicularenhancement material. For example, the tuning layer 194 may be made of asingle layer of MgO, Ta, Hf, W, Mo, Pt, or Pd. Alternatively, the tuninglayer 194 may have a bilayer structure (W/Ta) comprising a W sublayerformed adjacent to the magnetic free layer 154 or structure 122 and a Tasublayer formed adjacent to the compensation layer 196. Other exemplarybilayer structures, such as Ta/Ru, Ru/Ta, Ta/Hf, Hf/Ta, Ta/W, Ru/W,W/Ru, MgO/Ta, Ta/MgO, MgO/Ru, MgO/Hf, and MgO/W with the first of thetwo materials being disposed adjacent to the magnetic free layer 154 or130, may also be used for the tuning layer 194. Still alternatively, thetuning layer 194 may have a bilayer structure comprising an oxidesublayer, such as MgO, formed adjacent to the magnetic free layer 154 or130 and a thin conductive sublayer, such as CoFeB which may benon-magnetic or superparamagnetic. Additional tuning sublayers mayfurther form adjacent to the exemplary MgO/CoFeB tuning layer to formother tuning layer structures, such as but not limited to MgO/CoFeB/Ru,MgO/CoFeB/Ta, MgO/CoFeB/W, MgO/CoFeB/Hf, MgO/CoFeB/Ru/Ta,MgO/CoFeB/Ta/Ru, MgO/CoFeB/W/Ta, MgO/CoFeB/Ta/W, MgO/CoFeB/W/Ru,MgO/CoFeB/Ru/W, MgO/CoFeB/Hf/Ta, MgO/CoFeB/Ta/Hf, MgO/CoFeB/Hf/W,MgO/CoFeB/W/Hf, MgO/CoFeB/Hf/Ru, MgO/CoFeB/Ru/Hf, MgO/CoFeB/Ru/W/Ta,MgO/CoFeB/W/Ru/Ta, and MgO/CoFeB/Ru/Ta/Ru. As such, the tuning layer 194may comprise an insulating tuning sublayer formed adjacent to themagnetic free layer 130 or 154 and one or more conductive tuningsublayers formed adjacent to the insulating tuning sublayer.

It should be noted that the MTJ memory element of the present inventionmay be used in any suitable memory device, not just the conventionalmemory device illustrated in FIG. 1. For example, the MTJ memory elementof the present invention may be used in a novel memory device disclosedin U.S. Pat. No. 8,879,306 in which each MTJ memory element is coupledto two transistors.

The previously described embodiments of the present invention have manyadvantages, including high perpendicular anisotropy, minimum offsetfield, and improved anti-ferromagnetic coupling. It is important tonote, however, that the invention does not require that all theadvantageous features and all the advantages need to be incorporatedinto every embodiment of the present invention.

While the present invention has been shown and described with referenceto certain preferred embodiments, it is to be understood that thoseskilled in the art will no doubt devise certain alterations andmodifications thereto which nevertheless include the true spirit andscope of the present invention. Thus the scope of the invention shouldbe determined by the appended claims and their legal equivalents, ratherthan by examples given.

What is claimed is:
 1. A magnetic tunnel junction (MTJ) memory elementcomprising: a seed layer; and a magnetic fixed layer including a firstmagnetic fixed sublayer formed adjacent to said seed layer and a secondmagnetic fixed sublayer separated from said first magnetic fixedsublayer by a first perpendicular enhancement layer, said first andsecond magnetic fixed sublayers having a first fixed magnetizationdirection substantially perpendicular to layer planes thereof.
 2. TheMTJ memory element according to claim 1, wherein said seed layer is madeof a material comprising nickel and a transition metal with saidtransition metal being tantalum, titanium, zirconium, hafnium, vanadium,niobium, chromium, molybdenum, or tungsten.
 3. The MTJ memory elementaccording to claim 1, wherein said seed layer is made of a materialcomprising cobalt and a transition metal with said transition metalbeing tantalum, chromium, titanium, zirconium, hafnium, vanadium,niobium, molybdenum, or tungsten.
 4. The MTJ memory element according toclaim 1, wherein said seed layer is made of a material comprising ironand a transition metal with said transition metal being tantalum,chromium, titanium, zirconium, hafnium, vanadium, niobium, molybdenum,or tungsten.
 5. The MTJ memory element according to claim 1, whereinsaid seed layer is made of a material comprising nickel and tantalum. 6.The MTJ memory element according to claim 1, wherein said first magneticfixed sublayer has a multilayer structure formed by interleaving layersof a first type material with layers of a second type material, at leastone of said first and second type materials being magnetic.
 7. The MTJmemory element according to claim 6, wherein said first type material isCo or CoFe, said second type material is Ni, Pd, Pt, or any combinationthereof.
 8. The MTJ memory element according to claim 6, wherein saidsecond magnetic fixed sublayer has a multilayer structure formed byinterleaving layers of a third type material with layers of a fourthtype material, at least one of said third and fourth type materialsbeing magnetic.
 9. The MTJ memory element according to claim 1, whereinsaid second magnetic fixed sublayer has a multilayer structure formed byinterleaving layers of a third type material with layers of a fourthtype material, at least one of said third and fourth type materialsbeing magnetic.
 10. The MTJ memory element according to claim 9, whereinsaid third type material is Co or CoFe, said fourth type material is Ni,Pd, Pt, or any combination thereof.
 11. The MTJ memory element accordingto claim 1, wherein said first perpendicular enhancement layer is madeof chromium.
 12. The MTJ memory element according to claim 1, whereinsaid first perpendicular enhancement layer is made of tantalum, hafnium,titanium, zirconium, vanadium, niobium, molybdenum, or tungsten.
 13. TheMTJ memory element according to claim 1 further comprising ananti-ferromagnetic coupling layer formed adjacent to said secondmagnetic fixed sublayer opposite said first perpendicular enhancementlayer; a magnetic reference layer structure formed adjacent to saidanti-ferromagnetic coupling layer opposite said second magnetic fixedsublayer, said magnetic reference layer structure including one or moremagnetic reference layers having a second fixed magnetization directionthat is substantially perpendicular to layer planes thereof and issubstantially opposite to said first fixed magnetization direction; aninsulating tunnel junction layer formed adjacent to said magneticreference layer structure; and a magnetic free layer structure formedadjacent to said insulating tunnel junction layer opposite said magneticreference layer structure, said magnetic free layer structure includingone or more magnetic free layers that have a same variable magnetizationdirection substantially perpendicular to layer planes thereof.
 14. TheMTJ memory element according to claim 13, wherein said magneticreference layer structure includes a first magnetic reference layerformed adjacent to said anti-ferromagnetic coupling layer, a secondmagnetic reference layer formed adjacent to said insulating tunneljunction layer, and a second perpendicular enhancement layer formedbetween said first and second magnetic reference layers, said first andsecond magnetic reference layers having said second fixed magnetizationdirection substantially perpendicular to layer planes thereof.
 15. TheMTJ memory element according to claim 14, wherein said secondperpendicular enhancement layer is made of tantalum, hafnium,molybdenum, or tungsten.
 16. The MTJ memory element according to claim14, wherein said first magnetic reference layer is made of a materialcomprising cobalt and platinum.
 17. The MTJ memory element according toclaim 14, wherein said first magnetic reference layer has a multilayerstructure formed by interleaving layers of a fifth type material withlayers of a sixth type material, at least one of said fifth and sixthtype materials being magnetic.
 18. The MTJ memory element according toclaim 17, wherein said fifth type material is Co or CoFe, said sixthtype material is Ni, Pd, Pt, or any combination thereof.
 19. The MTJmemory element according to claim 14, wherein said second magneticreference layer is made of a material comprising cobalt, iron, andboron.
 20. The MTJ memory element according to claim 13, wherein saidmagnetic reference layer structure includes a first magnetic referencelayer formed adjacent to said anti-ferromagnetic coupling layer and asecond magnetic reference layer formed adjacent to said insulatingtunnel junction layer, said first and second magnetic reference layershaving said second fixed magnetization direction substantiallyperpendicular to layer planes thereof.
 21. The MTJ memory elementaccording to claim 20, wherein first magnetic reference layer is made ofa material comprising cobalt, iron, and tantalum.
 22. The MTJ memoryelement according to claim 20, wherein second magnetic reference layeris made of a material comprising cobalt, iron, and boron.